It is well known to use equipment having gases, particles, etc. flowing therethrough to accomplish various purposes such as manufacturing, analysis, testing, etc. Additionally it is known to observe such processes by various techniques as a simple window into the equipment, or by sophisticated analytical apparatus. For example, in the manufacture of semiconductors, integrated circuits, and the like, gas flow streams are often used to form layers upon a work piece or substrate, to etch off layers, and the like. These processes are often observed through protective windows. Additionally, in integrated circuit processing it is frequently desirable to monitor the process with an analytical apparatus. One common apparatus is an in situ particle counter which employs a laser beam positioned through the flow pathway. A detector measures the number of particles by sensing light scattering.
A problem with systems using an optical part such as a window or particle counter that depends on good optics for proper functioning is that not only will the gas molecules deposit on the substrate or work piece, they will deposit upon the optical part. Over a relatively short period of time, enough of a deposit is formed to impair vision or to interfere with the operation of the apparatus that requires excellent optics to perform its function.
Thus, there is a need for a way to restrict, inhibit or prevent the molecules from depositing on optical parts without otherwise obstructing the flow. That is, the method should optimally minimize flow restriction of other bodies, such as particles. For example, a device to prevent the transmission of molecules from clouding a particle counter would be useless if it also blocked the particles from coming through.